24 



THE AMERICAN MONTHLY 



[February, 



terial which binds them together, and 

 makes them readily separate when 

 pulled apart with needles. The soda 

 should be thoroughly washed out, 

 when the fibres may be allowed to 

 dry. 



The microscopical examination is 

 conducted in a mixture of equal parts 

 of water and glycerin. The fibres 

 are placed in the mixture or on a 

 slide, a ^-inch cover-glass applied, 

 and the examination conducted with 

 a I and a -1 objective. The genei"al 

 character of the fibre is thus quickly 

 made out, and if it should be one of 

 the more common forms, it would be 

 immediately recognized. If it should 

 be a fibre with which the observer is 

 not familiar, it is first examined care- 

 fully, the diameter of the fibres meas- 

 ured, and the appearance of the ends 

 particularly noted. The next step is 

 to treat it with reagents, unless it 

 should seem desirable to measure the 

 length of the fibres at this stage. The 

 length is measured by stretching some 

 of the fibres out on a slip of glass, in 

 water or glycerin, and measuring 

 their length in any convenient way. 



Two reagents are used in the ex- 

 amination of fibres, one a solution of 

 iodine, which is allowed to act for a 

 few moments, and then followed by 

 the second, which is sulphuric acid 

 of a certain strength. 



The iodine solution is prepared by 

 dissolving one gramme of potassium 

 iodide in loo c. c. of water, and add- 

 ing iodine to saturation, leaving a 

 portion of iodine undissolved in the 

 fluid to maintain its strength. 



The sulphuric acid solution is made 

 by mixing two volumes of glycerin 

 and one of water, and to this mix- 

 ture, kept cool by surrounding it with 

 cold water, is added with constant 

 stirring three volumes of commercial 

 sulphuric acid. 



When a fibre is treated in the man- 

 ner to be described with these two 

 reagents, it becomes colored either 

 blue or yellow, depending upon the 

 purity of its cellulose. Pure cellu- 

 lose is colored blue, but when mixed 



with matters which frequently ac- 

 company vegetable fibres, particu- 

 larly such as are hard and inelastic, 

 the blue color is concealed by the im- 

 purities, and various shades of yel- 

 low result. 



The strength and suppleness of a 

 fibre depends upon the purity of the 

 cellulose. The yellow color indicates 

 that the fibres are of a woody nature, 

 short, and brittle when bent, although 

 they may be strong in a longitudinal 

 direction. Among the most valuable 

 fibres giving a yellow reaction are the 

 New Zealand flax, Phormium tenax, 

 the bowstring hemp. Sansiviera zey- 

 laiiica., and the pita of our southern 

 countries, obtained from some of the 

 agaves, specimens of which can al- 

 ways be obtained from the leaves of 

 the common centurj' plant. Most of 

 the fibres from the palms also give 

 the yellow color. 



These reactions aflbrd a ready 

 means of separating fibres into two 

 classes, those which are colored blue 

 and those which are colored yellow. 

 M. V^tillart has made a further di- 

 vision, separating the mono- and di- 

 cotyledonous plants, certain ones of 

 each division taking the blue and 

 others the yellow. 



To apply the reagents a portion of 

 the dry fibre is placed on a slide, and 

 a few drops of the iodine solution 

 added to it. After a few moments 

 the liquid is removed by the use of 

 blotting-paper, which is caused to 

 absorb as much moisture as possible 

 by pressing it gently upon the fibres. 



The cover-glass is then applied, 

 and the sulphuric acid solution al- 

 lowed to flow under one side while a 

 piece of blotting-paper absorbs it on 

 the opposite side. The characteristic 

 color soon shows, even to the naked 

 eye, and the appearance of the fibres 

 under the microscope is almost sure 

 to lead to their identification. 



Among the fibres giving a yellow 

 reaction jute is the most common, 

 and will serve well for experimental 

 trials. Much of the coarse bagging or 

 sacking, burlaps, gunny-cloth, etc., 



